Field of the Invention
The present invention relates to a luminescent wheel, a light source unit having a luminescent wheel device including the luminescent wheel, and a projector including this light source unit.
Description of the Related Art
In these days, data projectors are used on many occasions as an image projection system which projects an image of a screen or a video image of a personal computer, as well as images based on image data which is stored on a memory card or the like on to a screen. In these data projectors, light emitted from a light source is caused to converge to a micromirror display device called a DMD (Digital Micromirror Device) or a liquid crystal panel so that a full-color image is displayed onto a screen.
In addition, the application of such projectors is expanding widely from commercial presentation to domestic use as video equipment including personal computers, DVD players and the like has been used generally. Conventionally, the mainstream of these projectors has been those which utilize a high-intensity discharge lamp as a light source. In recent years, however, there have been made various developments of projectors which use, as a light source, a plurality of semiconductor light emitting elements such as laser diodes and which include a luminescent wheel which uses the semiconductor light emitting elements as excitation light sources.
A projector disclosed in the Japanese Unexamined Patent Publication No. 2012-37681 includes a red light source device and a luminescent wheel device. The luminescent wheel device has a luminescent wheel having a luminescent material layer on to which light in the blue wavelength range which is emitted from an excitation light shining device is shone as excitation light to thereby emit luminescent light in the green wavelength rage and a diffuse transmission area which diffuses and transmits light emitted from the excitation light shining device. The excitation light shining device also functions as a blue light source since light emitted therefrom is diffused and transmitted through the diffuse transmission area of the luminescent wheel.
In the luminescent wheel of the luminescent wheel device which is disclosed in the Japanese Unexamined Patent Publication No. 2012-37681, an arc-shaped cut-out portion is cut in a disc-shaped metallic base, and a diffuse plate is provided in this cut-out portion. This luminescent wheel has the luminescent material layer which is provided in an end-to-end relationship with the diffuse plate in a circumferential direction, and the luminescent material layer is provided in an annular recess portion provided on the mirror finished base. Because of this, it is difficult to machine the metallic base to provide the annular recess portion, and a certain length of machining time is required. Further, the metallic base needs to have a predetermined thickness for forming the annular recess portion. This makes it difficult to form the cut-out portion through punching by using a press, and therefore, the cut-out portion is required to be formed through cutting. It is considered that forming the cut-out portion through cutting takes a certain length of time.
In recent years, a luminescent wheel 501 shown in FIG. 9 is used as a luminescent wheel in which the aforesaid problem with machining the metallic base is improved. In this luminescent wheel 501, a C-shaped partially annular luminescent material layer 502 is provided on a front side of a reflecting plate 510. A first diffuse plate supporting plate 530 is provided on a back side of the reflecting plate 510 so as to support a diffuse plate 520. The diffuse plate 520 is fastened by claw portions 533 which are provided at both ends of a cut-out portion in the first diffuse plate supporting plate 530 so as not to come off in a direction in which a centrifugal force is applied when the luminescent wheel 501 rotates.
Further, a second diffuse plate supporting plate 540 is provided on a back side of the first diffuse plate supporting plate 530. Additionally, a front side of the diffuse plate 520 near an inner circumferential edge 522 thereof is superposed on a back surface of the reflecting plate 510 near an inner circumferential edge 512 of a cut-out portion in the reflecting plate 510. On the other hand, a back side of the diffuse plate 520 near the inner circumferential edge 522 thereof is superposed on a front side of an inner circumferential edge 542 of a cut-out portion in the second diffuse plate supporting plate 540. In this way, the diffuse plate 520 is held by the reflecting plate 510 and the second diffuse plate supporting plate 540 to be fixed to the luminescent wheel 501.
Since the reflecting plate 510, the first diffuse plate supporting plate 530 and the second diffuse plate supporting plate 540 of the luminescent wheel 501 shown in FIG. 9 are each formed of a thin metallic plate, the cut-out portions and the like can be machined through punching. Further, since the luminescent wheel 501 is formed by combining these disc-shaped thin plate materials together, the fabricating work becomes easy.
However, the luminescent wheel 501 shown in FIG. 9 is configured as the four-layer construction of the first diffuse plate supporting plate 530, the second diffuse plate supporting plate 540, the reflecting plate 510 and the luminescent layer 502, and therefore, the thickness of the luminescent wheel 501 is increased, thereby calling for an enlargement in size of the luminescent wheel 501. Although it is considered to reduce the respective thicknesses of those constituent members, it is required that the reflecting plate 501 has a predetermined thickness so as to be prevented from being thermally deformed when the reflecting plate 501 is mirror finished. Additionally, since the first diffuse plate supporting plate 530 fastens the diffuse plate 520 with the claw portions 533 in relation to the direction in which the centrifugal force is applied, the predetermined thickness is required.